This application relates generally to color blend mixing, and in particular relates to sensing blend color homogeneity.
Modern plastic materials have found a wide range of markets and a variety of applications in diverse manufacturing fields. These plastic materials offer many desirable characteristics such as an excellent finish, desirable electrical, thermal and mechanical properties, low-cost and a variety of colors.
Plastics are typically formed of one or more base polymers or resins, one or more colorants, and other additives. Such additives may include, for example, fiberglass for structural reinforcement, flame retardents, plasticizers, or mold release agents. The plastics are manufactured by initially mixing these components to form a substantially homogeneous polymer blend. The polymer blend then typically undergoes extrusion, or the like, to form a raw product, for example pellets. The raw products are then utilized to produce final polymer products of various forms.
Recently, in the field of polymer design, there has been a demand for color polymer blend techniques that make it possible to faithfully reproduce blend colors. The color of the final product may depend on several factors including the concentration and type of colorant and base resin, temperature history during mixing, and the ultimate degree of constituent inter-mixing achieved during processing. Thus, variations in color between polymer products may arise for a variety of reasons.
For example, color may vary among products due to polymer product formulation or recipe differences. Color variations may exist between lots for a given product formulation or recipe due to machine-to-machine differences. Color differences may exist within lots due to changing raw material characteristics, changing operating conditions, and inaccuracies and other anomalies in processing, including speed rates.
Polymer color is typically manually adjusted by adjusting the amount of colorant for a given production run. The colorant may take any conventional form which affects the color of the polymer product by itself or in combination with other constituents. For example, solid pigments and liquid pigments or dyes may be used for affecting the color of the final product.
In a typical production process, the colorant and base resin are blended together and compounded or extruded in a laboratory machine to generate pellets. The pellets are then injection molded to obtain a plaque with substantially uniform color, which is then conventionally measured in a laboratory spectrocolorimeter. The measured plaque color is compared with a reference or standard plaque color, and differences therebetween are corrected by adjusting the colorant. The sequence is repeated until the plaque color falls within an acceptable range to the reference plaque.
A sample of the finally corrected colorant and resin blend is then compounded on a production scale machine that follows the same procedure as the laboratory machine to produce a color plaque which is again compared with a reference plaque. If required, the color in the production machine is suitably corrected to affect an acceptable match between the measured plaque and the reference plaque.
This process, therefore, requires many steps to achieve a desired color in the polymer pellets which increases processing time and cost. Accordingly, it is desired to improve the process of constituent inter-mixing in the production of a polymer product from base resins and colorants.